A study to investigate effects of pH, inoculum percentage and pulp density on the ferric ion production from pyrite using mixed mesophilic bacteria

Biological dissolution of pyrite leads to production of ferric ion and sulfuric acid. The produced ferric ion is a strong oxidant agent, which is able to dissolve different metal sulfides. This study aimed to examine effects of pH, pulp density and inoculation percent of bacteria on extraction rate of ferric iron ions from pyrite using a mixture of mesophilic bacteria. The pyrite sample was prepared from a pyrite lode in Midok copper mine. A mixture of mesophilic bacteria, including 40% Acidi thiobacillus ferrooxidans, 40% of  Acidithiobacillus thiooxidans and 20% of Leptasprillum ferrooxidans, was used for all leaching tests. According to results, effect of pH was more significant in bioleaching of pyrite and production of ferric ion than other factors. The maximum amount of produced ferric (1.93 g/l) was earned at pH 2, a pulp density of 25 g/l and inoculation percent of 15%. The desired amounts of byproducts of pyrite dissolution can be obtained by operational parameters such as pH, pulp density and inoculation percent in bioleaching. Thus, by taking into account the optimal conditions of mentioned parameters, it is possible to increase the production efficiency of valuable metals by hydrometallurgy processes of ferric ions.